Switchgrass nitrogen fertility response and nutrient cycling in a hay system

Authors: Ashworth, Amanda; Moore, Philip; KING, RANDY - Retired ARS Employee; DOUGLAS, JOEL - Natural Resources Conservation Service (NRCS, USDA); POTE, DAN - Collaborator; JACOBS, ALAYNA - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2020
Publication Date: 5/26/2020
Citation: Ashworth, A.J., Moore Jr, P.A., King, R., Douglas, J.L., Pote, D.A., Jacobs, A. 2020. Switchgrass nitrogen fertility response and nutrient cycling in a hay system. Agronomy Journal. 112:1963-1971. https://doi.org/10.1002/agj2.20156.
DOI: https://doi.org/10.1002/agj2.20156

Interpretive Summary: Switchgrass, a native grass that grows well under low nutrients and drought conditions, may be used in cattle operations for supplying potentially low-cost hay. Although, little information exists on appropriate various fertilizer rates for this forage crop. The purpose of this work was to gain greater insight into switchgrass yield response to nitrogen. Researchers determined what hay quality to expect per fertilizer rate. This study found that forage quality varied, but in general, intake and digestibility improved under greater N fertility. Breakeven analyses are need to be conducted to determine if yield increases from greater fertilizer-N are economical in a two-cut forage system.

Technical Abstract: Nitrogen (N) requirements for switchgrass (Panicum virgatum) forage production in the Mid-south are largely unknown, although data are needed for predicting break-even prices based on fertilizer response. This study determined switchgrass forage yield, quality, N removal, and soil fertility response in a two forage harvest (pre-anthesis) system after split applications of 0, 84, 168, 252, and 336 kg N ha-1 yr-1 from 2014-2016. Controls were represented by a no fertilizer and a 0 N rate with supplemental P, K, and S. For all experimental years, yield did not benefit from supplemental P, K, Mg, and S, suggesting N was the limiting nutrient. Yield also did not differ from the 252 or the 336 kg N ha-1 yr-1 rate (9.2 and 9.4 kg ha-1, respectively); therefore, growth was not improved beyond the 252 kg N ha-1 threshold in a two-cut forage system. At higher N fertility rates (336 kg N ha-1), the majority of soil nutrient concentrations were reduced compared to the 252 kg N ha-1 rate, perhaps owing to greater removal in harvested plant tissue. Tissue-N removal was greatest for the highest N application, albeit not different from the 252 kg N ha-1 rate; NUE had an inverse relationship with N removal, as it peaked during the lowest N application (84 kg N ha-1). Forage quality varied, but in general, intake and digestibility improved under greater N fertility. Quantifying trends in forage yield and quality based on N fertility are useful for economic and environmental trade-off analyses.